Successful gene therapy of cystic fibrosis (CF) or alpha1-antitrypsin inhibitor (AAT) deficiencies will require that patients immunologically tolerate gene grafts for the cystic fibrosis transmembrane conductance regulator (CFTR) or AAT. This proposal uses the mouse models to investigate mechanisms of natural and induced tolerance of CFTR and AAT. In Aim 1 we will determine the basis of non-H-2-linked tolerance of human AAT in the C57BL/6 mouse, and apply these lessons to the AAT.PiZ transgenic mouse strain, an immune model for the human AAT-deficiency. The most common mutant form of CFTR is deltaF508. deltaF508 has been identified as a severe folding mutant that degrades within the endoplasmic reticulum. It does not enter the endosomal compartment where antigen processing for class II major histocompatibility complex molecules and CD4+ T cells occurs. Such processing is required for self- tolerance. To develop means of inducing tolerance to CFTR in deltaF508 patients, Aim 2 uses CFTR knock-out and deltaF508 transgenic mice to determine mechanisms of deltaF508 antigen processing and induced tolerance of wild-type CFTR protein. Most forms of tolerance induction involve the induction of anergy or apoptosis in responding T or B cells. When T cells first recognize antigen they transiently become sensitive to killing by the "death ligands" tumor necrosis factor alpha (TNFalpha) and Fas ligand (FasL). Some tissues and tumors appear to resist T cell attack by expressing FasL ectopically, suggesting that co-expression of death ligands with therapeutic genes might induce tolerance of gene therapy. Experimental tests of this approach indicate efficient tolerance induction will require proper co-stimulation of T cells to induce sensitivity to FasL and TNFalpha. Aim 3 will improve the efficiency of FasL/TNFalpha- induced tolerance to gene therapy by determining the requirements of co- stimulation. These studies will provide information crucial to the success of gene therapy of the lung.